Requirements for robust IP/UDP/RTP header compression
RFC 3096
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(July 2001; No errata)
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RFC 3096 (Informational)
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Network Working Group M. Degermark, Editor
Request for Comments: 3096 University of Arizona
Category: Informational July 2001
Requirements for robust IP/UDP/RTP header compression
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document contains requirements for robust IP/UDP/RTP (Internet
Protocol/User Datagram Protocol/Real-Time Transport Protocol) header
compression to be developed by the ROHC (Robust Header Compression)
WG. It is based on the ROHC charter, discussions in the WG, the 3GPP
document "3GPP TR 23.922", version 1.0.0 of October 1999, as well as
contributions from 3G.IP.
1. Introduction
The goal of the ROHC WG is to develop header compression schemes that
perform well over links with high error rates and long link round
trip times. The schemes must perform well for cellular links built
using technologies such as WCDMA, EDGE, and CDMA-2000. However, the
schemes should also be applicable to other future link technologies
with high loss and long round trip times.
The following requirements have, more or less arbitrarily, been
divided into three groups. The first group deals with requirements
concerning the impact of an header compression scheme on the rest of
the Internet infrastructure. The second group concerns what kind of
headers that must be compressed efficiently. The final group
concerns efficiency requirements and requirements which stem from the
properties of the anticipated link technologies.
2. Header compression requirements
Several current standardization efforts in the cellular arena aim at
supporting voice over IP and other real-time services over IP, e.g.,
GERAN (specified by the ETSI SMG2 standards group), and UTRAN
Degermark Informational [Page 1]
RFC 3096 Requirements for IP/UDP/RTP ROHC July 2001
(specified by the 3GPP standards organization). It is critical for
these standardization efforts that a suitable header compression
scheme is developed before completion of the Release 2000 standards.
Therefore, it is imperative that the ROHC WG keeps its schedule.
2.1 Impact on Internet infrastructure
1. Transparency: When a header is compressed and then decompressed,
the resulting header must be semantically identical to the original
header. If this cannot be achieved, the packet containing the
erroneous header must be discarded.
Justification: The header compression process must not produce
headers that might cause problems for any current or future part of
the Internet infrastructure.
2. Ubiquity: Must not require modifications to existing IP (v4 or
v6), UDP, or RTP implementations.
Justification: Ease of deployment.
Note: The ROHC WG may recommend changes that would increase the
compression efficiency for the RTP streams emitted by
implementations. However, ROHC cannot rely on such recommendations
being followed.
2.2 Supported headers and kinds of RTP streams
1. IPv4 and IPv6: Must support both IPv4 and IPv6.
Justification: IPv4 and IPv6 will both be around during the
foreseeable future.
2. Mobile IP: The kinds of headers used by Mobile IP{v4,v6} should be
compressed efficiently. For IPv4 these include headers of tunneled
packets. For IPv6 these include headers containing the Routing
Header, the Binding Update Destination Option, and the Home Address
option.
Justification: It is very likely that Mobile IP will be used by
cellular devices.
3. Genericity: Must support compression of headers of arbitrary RTP
streams.
Degermark Informational [Page 2]
RFC 3096 Requirements for IP/UDP/RTP ROHC July 2001
Justification: There must be a generic scheme which can compress
reasonably well for any payload type and traffic pattern. This does
not preclude optimizations for certain media types where the traffic
pattern is known, e.g., for low-bandwidth voice and low-bandwidth
video.
Note: This applies to the RTP stream before as well as after it has
passed through an internet.
4. IPSEC: ROHC should be able to compress headers containing IPSEC
subheaders.
Note: It is of course not possible to compress the encrypted part of
an ESP header, nor the cryptographic data in an AH header.
2.3 Efficiency
1. Performance/Spectral Efficiency: Must provide low relative
overhead under expected operating conditions; compression efficiency
should be better than for RFC 2508 under equivalent operating
conditions. The error rate should only marginally increase the
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